1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a reflection type liquid crystal display having a reflection electrode provided with bumps and a method for fabricating the same.
2. Description of the Related Art
Cathode ray tubes (CRTs) used for displays like monitors of televisions or computers are not easy to install or move due to disadvantages of the larger, heavier, and power consumptive characteristics. To overcome such disadvantages, liquid crystal displays, plasma display panels, or flat panel displays using an electroluminescence element have been proposed and widely used.
High definition and multicolor display characteristics with less power consumption and lower voltage make the LCDs considered as one of most leading display device. In addition, LCDs are easy to manufacture, thus are widely used for various electronic devices.
There are two types of LCDs: a projection type display device using an external light source; and a reflection type display device using ambient lights.
The reflection type display is thin and light. It consumes less power because backlight devices are not necessary. It shows an excellent display outdoors. Thus, the reflection type displays are widely used for a portable device.
However, the current reflection type LCD has a dark screen and fails to show high definition and multicolor images. Therefore, the reflection type LCDs are employed for a low price product that requires a simple pattern display, such as, numbers.
To use a reflection type LCD for a portable information device with functions of a document viewer and an internet viewer, a high definition and a multicolor display with an enhanced reflection luminance are necessary. Such an enhancement in reflection luminance and high definition is also necessary to easily look at the monochromatic LCDs that mainly display character information. To achieve such an enhancement, it is necessary for the active matrix substrates to have switching elements, for example, thin film transistors. However, monochromatic LCDs have limits in displaying information, which may not call a high price. Therefore, thin film transistors having a high panel price may not be suitable for the monochromatic LCDs.
In the long run, it is required that the portable information devices are provided with a multicolor display function. The monochromatic LCDs will disappear, and the reflection type LCDs are under development to have a multicolor display function.
Despite the developing panel technologies and the expanding market, the reflection type multicolor LCDs are rarely available commercially. This is because the reflection type multicolor LCDs have a low performance in brightness, contrast, and a response time.
Two techniques are combined to obtain an improved brightness. One is enhancing a reflectivity of a reflection electrode, and the other is achieving a high aperture ratio. The reflectivity enhancement has been used for a conventional guest-host liquid crystal display device. Maximizing a reflectivity by allowing minute bumps to a reflection electrode is disclosed in U.S. Pat. No. 5,408,345 entitled xe2x80x9cReflection type liquid crystal display device wherein the reflector has bumpsxe2x80x9d.
However, the ideal reflectivity has not yet been achieved, always requiring a reflectivity enhancement for the reflection type liquid crystal display devices.
FIG. 1 is a schematic section view showing a reflection electrode of a conventional reflection type liquid crystal display device.
Referring to FIG. 1, a reflection electrode 4 of a conventional reflection type liquid crystal device has bumps where a convex portion 6a and a concave portion 6b occur alternately. However, bumps of reflection electrode 4 are simple. Therefore, as shown in the graph of FIG. 9, such a conventional reflection type liquid crystal device has an extremely low reflectivity of approximately 13% when the angle of the incident light is xe2x88x9230xc2x0 at which the reflectivity in general is the highest.
Reference numerals 2 and 6 denote a first insulation film and a second insulation film.
Moreover, in such a conventional method for forming a reflection electrode having bumps, an organic insulation film that is used for forming a bumpy organic insulation film pattern may not be photo-sensitive. Therefore, a first photolithography process for forming a contact hole to the organic insulation film, and a second photolithography process for forming bumps are required.
It is therefore an object of the present invention to enhance a reflectivity of a reflection electrode in a reflection type liquid crystal display device.
It is another object of the present invention to simplify a process for manufacturing a reflection electrode having bumps in a reflection type liquid crystal display device.
To achieve the above objects and other advantages, there is provided a reflection type liquid crystal display device that has a reflection electrode on its thin film transistor substrate. The reflection electrode has at its surface a convex portion and a concave portion. The top of the convex portion is caved or has a dimple. A method for fabricating a reflection type liquid crystal display is also provided. A photo-sensitive organic insulation film is used to form a bump to achieve a high reflectivity. A heat flow method is used for fabricating a bump on the insulative organic film. The present invention improves the reflectivity of the device and simplifies the manufacturing process.